1. Technical Field of the Invention
The present invention relates in general to optical MEMS, and in particular, to optical path retardation multiplier devices using MEMS technology.
2. Description of Related Art
Micro Electro-Mechanical Systems (MEMS) refers to the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through microfabrication technology. For example, the microelectronics are typically fabricated using an integrated circuit (IC) process, while the micromechanical components are fabricated using compatible micromachining processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical components. MEMS devices are attractive candidates for use in spectroscopy, profilometry, environmental sensing, refractive index measurements (or material recognition), as well as several other sensor applications, due to their low cost, batch processing ability and compatibility with standard microelectronics. In addition, the small size of MEMS devices enables the integration of equipment incorporating MEMS devices into mobile and hand held devices.
Recently, MEMS devices have been utilized in a number of optical applications that require large optical displacement by transforming a mechanical distance into an equivalent much larger optical distance. For example, MEMS technology can provide adequate resolution in many Fourier Transform spectrometers and Michelson interferometers. As another example, MEMS devices can produce sufficient scanning depths in various Optical Coherence Tomography (OCT) applications. In addition, MEMS devices can also be used to achieve dynamic optical focusing through the manipulation of the optical beam working distance by a moving MEMS mirror.
In the area of spectrometry in particular, silicon-MEMS Fourier-transform spectrometers have been introduced that achieve a resolution of about 50 nm around 1500 nm in the NIR (220 cm−1). In addition, MEMS-based Fourier transform-IR spectrometers for use in the 2-13.5 μm spectral range have also been proposed. The resolution targeted for such an IR spectrometer is 10 cm−1, which requires a minor motion on the order of 0.5 mm. However, even higher resolutions are needed in future MEMS based Fourier transform spectrometers. In order to achieve these higher resolutions, the optical path difference or optical path retardation must be increased. Unfortunately, such an increase is not compatible with the small mechanical displacements in existing compact size MEMS devices.
Therefore, what is needed is an optical MEMS device that allows obtaining a much longer optical path difference for a given mechanical displacement.